Electronic structure and properties of Bi2Sr2CaCu2O8, the third high-Tc superconductor

Abstract

Abstract Results of a highly precise local density determination of the electronic structure (energy bands, densities of states, Fermi surface and charge densities) of the new high-Tc superconductor Bi2Sr2CaCu2O8 are presented. The calculations employed the full-potential linearized augmented plane wave (FLAPW) method and the subcell structure parameters given by the work of Hazen et al. and Sunshine et al. As in the case of the other Cu-O superconductors, we find a relatively simple band structure at EF and strongly anisotropic highly 2D properties. The Sr and Ca atoms are highly ionic, with the Ca2+ ions serving to insulate the Cu-O planes. The Bi-O planes contribute substantially to N(EF), the density of states at EF, and to the transport properties whereas neither the Sr or Ca do. The N(EF) contribution from the Cu-O planes (∼1.0 states/eV-Cu atom) is lower (per Cu atom) than that found previously for the La-Sr-Cu-O and Y-Ba-Cu-O superconductors. The highly 2D Fermi surface shows regions of strong Cu-O and Bi-O hybridization from which highly anisotropic superconducting energy gaps are predicted. Here, too, an electron-phonon calculation of Tc (using the crude rigid ion approximation) is found to be inadequate. As in the case of YBa2Cu3O7-δ, strongly localized states at EF (arising from Bi-O and Cu-O) may be responsible for charge transfer excitations (excitons) which cause the high Tc.